The delivery of oligonucleotides and other cell membrane impermeable compounds into a living cell is highly restricted by the complex membrane system of the cell. Drugs used in antisense, RNAi, and gene therapies are relatively large hydrophilic polymers and are frequently highly negatively charged. These physical characteristics severely restrict their direct diffusion across the cell membrane. For this reason, the major barrier to polynucleotide therapeutic efficacy is the delivery of the polynucleotide across a cell membrane to the cell cytoplasm or nucleus.
One approach that has been used to deliver small nucleic acid in vivo has been to attach the nucleic acid to either a small targeting molecule or a lipid or sterol. While some delivery and activity has been observed with these conjugates, the very large nucleic acid dose required with these methods is impractical.
Considerable amount of literature evidence supports the hypothesis that the major hurdles for oligonucleotide delivery are cell uptake and endosomal escape. Small interfering RNAs (siRNA) can achieve selective knock-down of therapeutic targets by degradation of specific messenger RNA, provided the siRNA reaches the RNA Induced Silencing Complex (RISC) in the cell cytosol. Receptor-targeted siRNA constructs can be taken up by cell surface receptors and accumulate in subcellular vesicles termed endosomes. A small fraction of the siRNA traverses the endosomal membrane to reach the cytosol. The process, termed endosomal escape, is a major barrier to cytosolic delivery and higher potency of siRNA therapeutics.
There remains a need for additional compositions or delivery methods that can provide effective in vivo delivery, cell uptake and/or endosomal escape of oligonucleotides.